U.S. patent number 5,762,630 [Application Number 08/772,401] was granted by the patent office on 1998-06-09 for thermally softening stylet.
This patent grant is currently assigned to Johnson & Johnson Medical, Inc.. Invention is credited to Robert Bley, Glenn Kubacki.
United States Patent |
5,762,630 |
Bley , et al. |
June 9, 1998 |
Thermally softening stylet
Abstract
The present invention describes a stylet that softens
dramatically upon insertion into a living body with a temperature
of about 37.degree. C. The stylet has a distal end and a proximal
end. Upon insertion of the distal end into a living body, the
distal end softens from a stiffness of about 78 Durometer Shore D
units to 25 Durometer Shore D units in a preferred embodiment.
Moreover, the proximal end of the stylet, which is not inserted
into the living body, retains its stiffness to aid a physician or a
nurse in inserting and placing the catheter and stylet
assembly.
Inventors: |
Bley; Robert (Menlo Park,
CA), Kubacki; Glenn (Cupertino, CA) |
Assignee: |
Johnson & Johnson Medical,
Inc. (Arlington, TX)
|
Family
ID: |
25094947 |
Appl.
No.: |
08/772,401 |
Filed: |
December 23, 1996 |
Current U.S.
Class: |
604/164.01;
600/585; 604/264; 604/272; 604/524; 604/531 |
Current CPC
Class: |
A61L
29/14 (20130101); A61M 25/0009 (20130101); A61M
25/0054 (20130101); A61M 2025/0064 (20130101) |
Current International
Class: |
A61L
29/00 (20060101); A61M 25/00 (20060101); A61L
29/14 (20060101); A61M 005/178 () |
Field of
Search: |
;604/110,158,164,264-5,280,272 ;128/768,772 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Shirai et al., "Development of Polymeric Shape Memory Material,"
Nagoya Research & Development Center, MTB 184, Dec. 1988, pp.
1-5. .
Memry Technologies, Inc., "Shape Memory Polymer," (11 pages). .
Mitsubishi Heavy Industries, Ltd., "Processing Instructions for
Mitsubishi Shape Memory Polymer," No. 1, Rev. 2.2, Apr. 1992, pp.
1-23..
|
Primary Examiner: Rimell; Sam
Assistant Examiner: Racunas; Robert V.
Attorney, Agent or Firm: Blakely, Sokoloff, Taylor &
Zafman
Claims
We claim:
1. A catheter stylet having a proximal end and a distal end,
comprising:
an elongated member having a substantially uniform cross-section
and a cross-sectional area, wherein upon insertion of the distal
end into a living body, the distal end of the stylet softens by at
least a factor of three in response to a body temperature of the
living body and substantially maintains the cross-sectional
area.
2. The stylet of claim 1, wherein upon insertion of the distal end
into the living body, the distal end of the stylet softens by at
least 50 Durometer Shore D units.
3. The stylet of claim 1, wherein the distal end softens in a few
seconds after being inserted into the living body.
4. The stylet of claim 1, wherein the elongated member has a glass
transition temperature of approximately 35.degree. C.
5. The stylet of claim 1, wherein a component has been added to the
elongated member to modify the stiffness throughout the elongated
member.
6. The stylet of claim 1, wherein a component has been added to the
elongated member to modify the stiffness at least at one point in
the elongated member.
7. A vascular access device, comprising:
a catheter having a lumen; and
a stylet having a cross-sectional area and a physical property such
that the stylet is capable of softening by at least a factor of
three and substantially maintaining the cross-sectional area when
exposed to a predetermined temperature, wherein the stylet is
disposed within the lumen of the catheter.
8. The vascular access device of claim 7, wherein the catheter also
softens when exposed to the predetermined temperature by at least
50 Durometer Shore D units.
9. The vascular access device of claim 7, wherein the predetermined
temperature is about 35.degree. C.
10. The vascular access device of claim 7, wherein the stylet
comprises a distal end and a proximal end and wherein upon
insertion of the distal end into a living subject, the distal end
softens.
11. The vascular access device of claim 10, wherein the distal end
of the stylet softens in a few seconds when inserted into the
living subject.
12. The vascular access device of claim 10, wherein the distal end
of the stylet softens so that its stiffness decreases at least 50
Durometer Shore D units.
13. The vascular access device of claim 8, wherein the stylet has a
distal end and a proximal end, and wherein upon insertion of the
distal end into a living body and exposure to the predetermined
temperature of approximately 35.degree. C., the distal end of the
stylet softens.
14. The vascular access device of claim 7, wherein a radiopacifier
has been added to the stylet.
15. The vascular access device of claim 14, wherein the
radiopacifier is selected from a group consisting of barium
sulfate, bismuth subcarbonate, bismuth trioxide, tungsten and
tantalum.
16. A stent stylet comprising:
an elongated member having a proximal end and a distal end and a
substantially uniform cross-section, the distal end of the stylet
having a physical property such that upon insertion into a living
body, the distal end of the stylet softens by at least a factor of
three in response to a body temperature of the living body.
17. The stent stylet of claim 16, wherein upon insertion of the
distal end into the living body, the distal end of the stylet
softens by at least 50 Durometer Shore D units.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to medical devices. More
specifically, the present invention pertains to a stylet that is
disposed within a medical device, such as a catheter.
2. Description of Related Art
Catheters are used to extract and/or infuse a fluid into a living
subject, such as a human patient. It is well-known that it is
desirable for a catheter to have a certain amount of stiffness to
aid insertion. Catheters are, however, often made of a soft,
pliable, bio-compatible material, such as polyurethane. As a
result, a metal stylet is often placed inside the catheter to
provide stiffness. This stiffness is required to quickly and easily
insert the catheter into a patient. Thus, the stylet is one method
of providing stiffness to aid insertion of the catheter.
But it is also desirable for a catheter to have the ability to
soften and/or expand once inserted to reduce patient trauma and to
increase patient comfort. This is especially important for
peripherally inserted central catheters (PICCs) that remain in a
patient for long periods of time, for example, two weeks to a
month. Several solutions are well-known in the prior art. One
answer is to form the catheter or part of the catheter from a
hydrophilic polymeric component that softens and/or swells when the
catheter is substantially hydrated inside the patient. This
softening process can require anywhere from an hour to several
hours and in some cases, a few days to be complete. Consequently,
the catheter did not soften and/or expand until after the catheter
had been completely inserted and placed in its final indwelling
point. See, e.g., U.S. Pat. No. 4,911,691 by Anuik et al. for an
"Assembly For Administering IV Solution", which is assigned to
Menlo Care. Thus, the initial insertion and placement of the
catheter occurred without the benefit of a softer catheter.
Another prior art solution is to form the catheter or part of the
catheter out of a thermally-softening polymeric material. In some
cases, the thermally-softening material also had a shape memory
component, so upon exposure to a predetermined heightened
temperature, the catheter softened and/or expanded and/or returned
to a predetermined shape. Typically, the thermally-softening
polymeric material used had a glass transition temperature
(T.sub.g) near the patient's body temperature. Upon exposure to its
T.sub.g, the thermally-softening material typically softens at
least 25 Durometer Shore D points. This softening process usually
lasts about a few seconds.
All of the prior art solutions focused on having a softer catheter
inside the patient, especially for those situations when the
catheter remains in a patient for several weeks. Unfortunately, the
catheter's softness during insertion is limited by a metal stylet,
which is typically placed within the catheter to aid insertion and
placement of the catheter. In particular, the metal stylet is
necessary to guide and insert the pliable catheter, such as a
longer-line catheter (e.g., a PICC) that must travel from
six-to-twenty inches inside the patient. Thus, regardless of the
softness of the catheter, the patient could still be affected by
the metal stylet during insertion and placement of the catheter and
stylet assembly. Thus, none of the prior art solutions considered
making a softer stylet to achieve greater patient comfort during
the insertion and placement of the stylet and catheter assembly.
This is because a stiff stylet has been believed to be essential to
insert and to place the soft pliable catheter. Consequently, during
the tortuous path of twists and turns to reach the catheter's final
indwelling point, the metal stylet may traumatize or damage the
patient's blood vessel, or perforate the catheter. Thus, a softer
stylet that increases patient comfort during the insertion and
placement of the stylet and catheter assembly is desirable. It is
also desirable that the softer stylet still be stiff enough outside
the patient to facilitate inserting and placing the catheter into
the patient.
SUMMARY
The present invention describes a stylet to aid insertion and/or
placement of a catheter by quickly softening when the stylet is
placed or inserted inside a living subject. In one embodiment, the
stylet is an elongated member having a proximal end and a distal
end. Upon inserting the distal end of the stylet into a living
subject, the distal end quickly softens in response to the higher
temperature (or warmth) of the living body. In contrast, the
proximal end of the stylet, which is outside the living subject,
does not soften but maintains its stiffness. Since the stylet is
often placed within a catheter, for example a PICC, that must
travel from six to twenty inches before reaching its final
indwelling point, a softened stylet should help minimize vessel
trauma and increase patient comfort. In addition, a softer stylet
decreases the possibility of patient trauma during the insertion
and placement of the stylet and catheter assembly. In a preferred
embodiment, the stylet can be made of a shape memory polymer
MM-3510 that is produced by Mitsubishi Heavy Industries, Ltd. and,
which has a glass transition temperature (T.sub.g) of 35.degree. C.
At 35.degree. C., shape memory polymer MM-3510 decreases in
stiffness from approximately 78 Durometer Shore D units to 25
Durometer Shore D units.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is illustrated by way of example and not by
way of limitation in the figures of the accompanying drawings in
which like references indicate similar elements. In addition, for
the sake of clarity, certain elements in a figure may appear larger
and are not drawn to scale.
FIGS. 1A-1E illustrate one embodiment of the present invention.
FIG. 2 is a graph showing how the material used in one embodiment
changes at its glass transition temperature (T.sub.g).
DERAILED DESCRIPTION
A thermally-softening stylet for reducing vessel trauma and
increasing patient comfort as the stylet and catheter assembly are
inserted and placed in a patient is described. In the following
description, numerous specific details are set forth in order to
provide a thorough understanding of the present invention. It will
be apparent, however, to one skilled in the art that the present
invention may be practiced without these specific details. In other
instances, well-known structures may not be shown in order to avoid
unnecessarily obscuring the present invention. In other cases,
specific examples are described and shown in order to thoroughly
describe the invention. It will be appreciated that these specific
examples are for the purpose of explanation and that alternative
embodiments will be understood by those in the art.
The present invention provides several advantages over the prior
art. The stylet of the present invention softens dramatically upon
insertion into a living subject, such as a human patient. Since a
catheter can be very thin, the patient can feel the catheter and
stylet assembly as it is inserted and manipulated through the
patient's blood vessels. In addition, although not perceptible to
the patient, a certain amount of vessel trauma may occur. Unlike
some prior art materials, which only considered softening the
catheter, the present invention also considers the impact of the
stylet's stiffness on the patient. Unlike prior art catheter
materials that softened in an hour, a few hours or even days, the
distal (i.e., inserted) end of the stylet softens almost
instantaneously upon insertion into the patient. Thus, the patient
receives the benefit of a softer stylet during the insertion and
placement of the stylet and catheter assembly, which together form
a vascular access device.
Moreover, because the stylet softens dramatically, the stylet and
catheter assembly is less likely to irritate and perhaps perforate
the patient's blood vessel. Since the stylet is also less likely to
perforate the catheter, the possibility of fluid leakage from the
catheter before the catheter reaches its final indwelling point
also decreases.
Finally, unlike prior art catheter materials, the material used to
form the present stylet does not expand substantially upon
insertion and exposure to the patient's body temperature. Thus,
because the stylet does not expand substantially when it softens,
the stylet is easy to remove and the fluid flow area inside the
catheter does not decrease. If the stylet expanded upon insertion
in the patient's body, the fluid flow area would decrease in
proportion to the increased size of the stylet. This causes
manipulation and removal of the stylet to be more difficult, if not
impossible, due to increased friction between the stylet and the
catheter. All of this can result in greater patient discomfort and
the possibility of the stylet perforating the catheter. In
addition, the stylet and catheter assembly could possibly damage
the blood vessel. These problems are avoided because the stylet of
the present invention does not use the prior art softening and
expandable material and thus, does not expand upon insertion in the
patient.
One embodiment of the present invention is illustrated in FIGS.
1A-1E. FIGS. 1A-1E illustrate the placement of a long-line
catheter, for example a PICC, into a blood vessel 101. A needle 109
is used to make the initial cut through the skin 100 as shown in
FIG. 1A. Once the needle 109, the introducer 103 and its sheath 107
are in the patient's vessel 101, the needle 109 is removed and
introducer 103 remains. The introducer 103 is comprised of a handle
105 coupled to a sheath 107.
In FIG. 1B, a catheter 111 having a stylet 113 disposed within it
is passed through the introducer 103 and into the patient's vessel
101. The catheter 111 and stylet 113 assembly are both gradually
inserted and placed in patient's vessel 101. Stylet 113 remains
stiff during the initial insertion, but softens quickly (e.g., a
few seconds) at its distal end upon insertion of the distal end
into the patient and exposure to the patient's body temperature. A
break is shown in the catheter 111 to illustrate the fact that the
entire length of the catheter 111 is not shown in FIG. 1B. The
catheter 111 is attached at its proximal end to a catheter hub 115,
which in turn is shown coupled to the stylet hub 117. It will be
appreciated that a stylet hub may not always be present. The
catheter hub 115 and the stylet hub 117 are used to help insert and
place the catheter 111 and stylet 113 assembly in the patient's
vessel 101.
Once the catheter 111 is properly placed in the patient's vessel
101, the introducer 103 is removed from its location in the patient
as shown in FIG. 1C. The sheath 107 is removed from the patient's
vessel 101. The two breaks shown in catheter 111 illustrate the
fact that the entire length of catheter 111 is not shown. In FIG.
1D, the introducer 103 is divided or peeled away and removed from
the area. It is to be noted that the introducer 103 may also be
peeled away from the catheter 111 while the introducer 103 is being
removed. To facilitate the peeling away and removal of the
introducer 103, the introducer handle 105 and sheath 107 may be
made of a durable material of varying thickness. Once the catheter
111 and stylet 113 has reached its final indwelling point in the
patient's vessel 101, the stylet is removed from the patient's
vessel 101 and catheter 111 using the stylet hub 117. The catheter
111 is left in the patient's vessel 101. It will also be
appreciated by one of skill in the art that the catheter 111 may be
made of silicon, polyurethane, a thermally-softening material, a
shape-memory material or any other bio-compatible material.
Although the stylet 113 is shown having a circular cross-section,
it will be apparent that the stylet 113 may also have a variety of
different configurations, for example, a substantially rectangular
or elliptical cross-section. See, e.g., co-pending application, "A
Stiffening Member To Increase Fluid Flow Within A Medical Device"
that is also assigned to Johnson & Johnson Medical, Inc. Stylet
113 has a proximal end and a distal end. Upon insertion of the
distal end of the stylet 113 within the catheter or outside of the
catheter into the living subject, the stiffness of the distal end
can decrease by at least 25 Durometer Shore D units or points. The
stylet 113 softens almost instantaneously or within about a few
seconds after it is exposed to the patient's body temperature. In
most cases, the patient is a human with a body temperature of
approximately 37.degree. C.
The proximal end of the stylet (e.g., attached to stylet hub 117),
and which is not inserted into the living subject, retains its
current stiffness and does not soften. Because the proximal end
remains stiff at room temperature, the attending physician or nurse
is able to push against the proximal end of the stylet outside the
patient to aid insertion through the introducer 103 and if present,
its internal valve, which can cause the greatest resistance to
catheter 111 and stylet 113 assembly insertion. In contrast, the
distal end inside the patient is pliable and easily manipulated
along the patient's blood vessel. This results in less potential
vessel trauma and discomfort for the patient. In a preferred
embodiment, the stylet can be made of a polyurethane-based shape
memory polymer that is produced by Mitsubishi Heavy Industries,
Ltd. and is available exclusively through Memry Technologies, Inc.
located at 57 Commerce Drive, Brookfield, Conn. 06804.
In a preferred embodiment, the stylet of the present invention can
be made of a shape memory polymer known as MM-3510, which is
available from Memry Technologies, Inc. located in Brookfield,
Conn. Referring to FIG. 2, a graph illustrates how the hardness or
stiffness of a stylet (made of MM-3510) changes in response to
increasing temperatures, in particular at its glass transition
temperature (T.sub.g). MM-3510 is a shape memory polymer that is
available in extrudable form and has a glass transition temperature
of about 35.degree. C. The glass transition point describes a
unique property of glasses and polymers. Unlike metals, glasses and
polymers do not crystallize on solidification. Instead, glasses and
polymers, such as MM-3510, preserve the amorphous structure of a
supercooled liquid in the glassy state 200. The glass transition
point is the temperature at which the shape memory polymer or glass
makes the transition 202 between a supercooled liquid and a glassy
solid.
MM-3510 is in the glassy region 200 with a stiffness of 78 Shore D
when it is exposed to a temperature below 35.degree. C., its glass
transition temperature (T.sub.g). The glassy region 200 ranges
between about 15.degree. C. to 35.degree. C. During its glass
transition region 202, which occurs at approximately 35.degree. C.,
the stiffness of material MM-3510 changes from about 78 Durometer
Shore D to about 25 Durometer Shore D. Thus, at around 35.degree.
C., which is its T.sub.g, MM-3510 becomes increasingly flexible and
soft as it enters the glass transition region 202 and then rubbery
region 204. The rubbery region 204 (for MM-3510) ranges between
approximately 35.degree. C. to 55.degree. C. As the temperatures
continue to increase beyond 55.degree. C., it will enter into a
fluid region 206.
Since the body temperature of most humans is about 37.degree. C.,
shape memory polymer MM-3510 is perfect for use in forming a stylet
or a catheter, which can be inserted into the human body. A stylet
or catheter formed from shape memory polymer MM-3510 will
dramatically soften within a few seconds upon insertion into a
human body. It will be apparent to one of skill in the art that the
stylet of the present invention may be made of other materials that
have properties similar to shape memory polymer MM-3510. These
properties include the temperature point (e.g. T.sub.g) at which
the material significantly softens.
It will also be appreciated that additional components, such as
polyurethane, polyurethane-based polymers and various
thermoplastics, may be added to shape memory polymer MM-3510 to
achieve a greater stiffness in the stylet at certain points or
throughout the entire stylet, or to achieve greater flexibility at
other points during the insertion and placement of the stylet. It
will also be apparent to one skilled in the art that the shape
memory component of the present invention can be heated above its
glass transition temperature and then formed into a desired shape,
for example, a substantially rectangular stylet. See, e.g.,
co-pending application, "A Stiffening Member To Increase Fluid Flow
Within A Medical Device" that is also assigned to Johnson &
Johnson Medical, Inc. Thus, the use of the shape memory polymer
MM-3510 to form the stylet of the present invention is meant to be
illustrative and not limiting.
It will be apparent to one skilled in the art that a radiopacifier
can be impregnated or added to shape memory polymer MM-3510 before
extruding the stylet. The radiopacifier helps the stylet to be more
visible on X-ray. Some exemplary radiopacifiers are barium sulfate,
bismuth subcarbonate, bismuth trioxide, tungsten and tantalum.
It will be noted the present invention may be used in a medical
device, other than a catheter. For example, the present invention
can be used with a stent, or any other device that would normally
require a guidewire or a stylet or a scope.
The foregoing description provides an example of a stiffening
member, such as a stylet, disposed within a medical device, such as
a PICC. It will be appreciated that numerous modifications may be
made in practicing the present invention without departing from the
spirit and scope of the invention, which is defined by the
following claims.
* * * * *